Standardize orthogonal CI buckets and reusable notebook checker

[acgetchell]

Goal

Align causal-triangulations with the shared validation shape: just ci should be the GitHub-equivalent flat union of leaf validators, and notebook validation should keep the current strong behavior while moving more logic into a reusable checker CLI.

Deliverables

• Make just ci compose leaf validators directly instead of depending on broad nested bundles.
• Keep focused changed-surface validators for local work: docs/config/Python/notebooks/core Rust/unit tests/doctests/integration tests/benchmarks/examples.
• Keep test-unit, test-doc, and test-integration as focused recipes for local or changed-surface validation.
• Add a broad Rust CI nextest bucket, for example test-rust-ci, that runs lib unit tests and integration tests together with cargo nextest run --release --profile ci --lib --tests.
• Wire just test-rust and just ci through test-rust-ci plus the separate doctest bucket, rather than compiling unit tests in the default profile and integration tests again in release.
• Keep doctests as their own bucket because cargo test --doc is not covered by nextest.
• Keep broad all-target Clippy sweeps as optional manual recipes outside just ci if they duplicate tests/examples/benches that have their own validators.
• Document the fast-cycle guidance: run the smallest changed test/doctest/integration crate first; compose focused buckets once for final non-core changes; run full just ci for core Rust or GitHub-equivalent validation.

Keep from the current notebook workflow

causal-triangulations already has the right notebook behavior:

• source notebooks must not commit outputs or execution counts
• notebook code is linted/type-checked after extraction
• fast notebooks execute headlessly in CI
• executed notebooks/artifacts are written under target/notebooks
• slow notebooks stay in an explicit notebook-check-slow bucket

Standardize

• Move output hygiene, JSON validation, cell compilation, extracted-code Ruff/ty checks, and diagnostics into a reusable scripts/notebook_check.py CLI.
• Keep Just recipes responsible for launch/headless execution policy: notebook, notebook-lint, notebook-check, notebook-check-slow, notebook-clear-outputs-all.
• Make just ci compose leaf validators directly rather than depending on broad nested bundles that may duplicate target classes.

Desired validation buckets

• GitHub Actions
• Markdown
• TOML
• YAML/CFF
• Python
• notebooks
• core Rust
• Rust focused tests: unit, doctest, integration recipes for changed-surface validation
• Rust broad CI tests: one release-profile nextest bucket for lib unit + integration tests, plus separate doctests
• benchmark harness compile
• examples

CI shape

Broad all-target Clippy sweeps can remain as optional manual recipes, but should not make just ci compile tests/examples/benches before their own validators run. Avoid the debug-plus-release Rust test split in broad CI: --lib and --tests select different target classes, but running them in different profiles recompiles the library twice. For scientific correctness and less duplicate compilation, broad Rust CI should use one release-profile nextest pass for lib unit + integration tests.

[acgetchell]

Update from the delaunay CI test-wiring pass: keep focused recipes for local/changed-surface validation (test-unit, test-doc, test-integration), but broad Rust workflows should avoid the debug-plus-release profile split. Add a CI Rust nextest bucket such as test-rust-ci and wire just test-rust / just ci through cargo nextest run --release --profile ci --lib --tests, with doctests remaining in their separate just test-doc bucket. Rationale: --lib and --tests select different target classes, but running unit tests in the default test profile and integration tests in release recompiles the library in both profiles. For scientific correctness and less duplicate compilation, broad CI should use one release-profile nextest pass for lib unit + integration tests.